The present invention relates generally to cardiac pacing. More particularly, the invention describes multiple embodiments of a single-conduit multi-electrode cardiac pacemaker configured for stimulating the bundle of His and surrounding areas for pacing the entire heart and methods of using thereof.
In a healthy heart, a heartbeat originates in a specialized cardiac conduction system and spreads via this system to all parts of the myocardium. The structures that make up the conduction system are the sinoatrial node (SA node), the internodal atrial pathways, the atrioventricular node (AV node), the bundle of His and its branches, and the Purkinje system. Activation spreads quickly across the atria to the AV node, which then delays the wave of excitation. The delay enables the atria to contract before the ventricles contract. After the activation is delayed by, and leaves, the AV node, it enters and excites the bundle of His. This excitation of the bundle of His spreads in a precise pattern to the ventricles through the ventricular conduction system composed of Purkinje fibers. Excitation spreading through this system activates each ventricular cell at a precise time to produce a coordinated ventricular contraction. These events are seen generally as a normal QRS signal composed of group of waveforms on electrocardiogram (ECG) representing ventricular depolarization.
For various reasons, this process of normal propagation of the electrical excitation wave throughout the heart may be disrupted leading to a variety of conduction abnormalities and subsequently to abnormal heart contractility. Many such abnormalities may be seen on the ECG signal and can be detected as distorted or absent P-wave or QRS signal. Such abnormalities may be treated by using an implantable cardiac pacemaker configured to generate artificial pacing signals when natural excitation/conduction is disrupted or absent altogether.
Traditional pacemakers include typically 2 or 3 individual wires or leads that extend separately to different chambers of the heart and provide electrical stimulation from different locations within the heart. In modern pacemakers, each individual electrode may be activated in a unipolar mode using the body of the implanted pacemaker itself for example as a ground electrode. More recently, a bipolar mode of electrode activation is used in which each individual lead is equipped with a second ring electrode (usually serving in an anode capacity) which may be spaced apart from the negative (cathode) electrode. The ring electrode may or may not be in touch with the cardiac tissue but still supports the activation of the main electrode via conduction through blood in the vicinity thereof.
Recent experience with cardiac pacing indicates that traditional pacing sites may not be ideal for a good number of patients. Particularly, this is the case for right ventricular pacing, which may result in decline in heart function in some patients due to asynchronous cardiac contraction. Therefore, new direction in pacing is needed to avoid asynchronous cardiac contraction. This was attempted by pacing directly into the natural conduction system of the heart and more specifically—stimulating the bundle of His. This area is located right in the center of the heart in close proximity to atrial and ventricular tissue—and therefore may allow stimulation of one or multiple chambers of the heart from essentially the same location.
Permanent His bundle pacing (PHBP) has a potential to be used for treatment of at least some of the conduction abnormalities such as for example intra- and infra-hisian block including a complete heart block and left bundle branch block (Barba-Pichardo R, Moriña-Vázquez P, Venegas-Gamero J, Maroto-Monserrat F, Cid-Cumplido M, Herrera-Carranza M. [Permanent His-bundle pacing in patients with infra-Hisian atrioventricular block]. Rev EspCardiol. 2006; 59(6):553-558; Lustgarten D L, Calame S, Crespo E M, Calame J, Lobel R, Spector P S. Electrical resynchronization induced by direct His-bundle pacing. Heart Rhythm. 2010; 7(1):15-21; Kronborg M B, Mortensen P T, Gerdes J C, Jensen H K, Nielsen J C. His and para-His pacing in AV block: feasibility and electrocardiographic findings. J Interv Card Electrophysiol. 2011; 31(3):255-262; Sharma P S, Vijayaraman P. His Bundle Pacing Or Biventricular Pacing For Cardiac Resynchronization Therapy In Heart Failure: Discovering New Methods For An Old Problem. J Atr Fibrillation. 2016; 9(4):1501; Herweg B, Gerczuk P Z, Sofi A, Vijayaraman P, Barold S S. Permanent His Bundle Pacing in Intra-Hisian Conduction Block: Mechanistic Insights. J Electrocardiol. 2017; 50(6):933-936.).
In patients undergoing pacemaker implantation, PHBP was found to be associated with reduction in death or heart failure hospitalization during long-term follow-up compared to a more conventional right ventricular pacing. Bundle of His pacing was also associated with higher rates of lead revisions and generator change. (Vijayaraman P, Naperkowski A, Subzposh F A, et al. Permanent His-bundle pacing: Long-term lead performance and clinical outcomes. Heart Rhythm. 2018:15(5); 696-702). In patients with heart failure and left bundle branch block, PHBP, as an alternative means to achieve cardiac resynchronization, has been shown to be feasible (Lustgarten D L, Crespo E M, Arkhipova-Jenkins I, et al. His-bundle pacing versus biventricular pacing in cardiac resynchronization therapy patients: A crossover design comparison. Heart Rhythm. 2015; 12(7):1548-1557) and possibly beneficial compared to biventricular pacing (Sharma P S, Dandamudi G, Herweg B, et al. Permanent His-bundle pacing as an alternative to biventricular pacing for cardiac resynchronization therapy: A multicenter experience. Heart Rhythm. 2018; 15(3):413-420).
Despite the recent technological progress with the design of electrophysiology (EP) mapping catheters and pacing leads, their ability to reliably reach the target area at and surrounding the bundle of His in patients with broad anatomical variations is very limited.
Currently, successful placement of the pacing lead to a bundle of His is only achieved in approximately 80% of the cases (Vijayaraman P, Dandamudi G, Zanon F, et al. Permanent His bundle pacing: Recommendations from a Multicenter His Bundle Pacing Collaborative Working Group for standardization of definitions, implant measurements, and follow-up. Heart Rhythm. 2018; 15(3):460-468). This is frequently due to the inability to attach the electrode to a successfully identified target site with a reasonable capture threshold. To this day, the area to deploy the pacing electrode is identified by traditional methods of a multipolar electrode catheter used as a rough guide in a point-by-point electrogram mapping. Additionally, determination of the bundle of His capture is not always clear or easy to determine clinically.
Conventionally, a single electrode is used for probing and searching for the best position for implantation. Such probing procedure uses a temporary attachment of the electrode to the endocardial surface of the cardiac tissue followed by successive cardiac stimulation starting at higher voltages and subsequently reducing the voltage until the response of the cardiac tissue is no longer observed on the ECG—so as to determine a threshold for the lowest effective stimulation voltage. If the desired ECG response cannot be achieved at all or can be achieved only at high voltages, the electrode is disconnected from the tissue and moved to another location where the process is repeated again. As more than one cardiac chamber stimulation is frequently desired, this process may be time consuming and may involve large number of fluoroscopy images—leading to increased radiation exposure for both the patient and the physician.
The lead placement therefore is dependent on a point-by-point mapping and pacing using a trial-and-error methodology. The need therefore exists for better pacing tools and pacing leads to achieve a more rapid and effective permanent cardiac pacing. The need also exists to resolve a guidance problem of the pacing leads and achieve a reproducible navigation to predetermined capture sites—so as to improve the operator's confidence, expedite the process of lead implantation and reduce radiation exposure due to excessive fluoroscopy imaging.